In addition to normal speech and data transmission, mobile communication systems provide a plurality of supplementary services for subscribers. Basic services according to the specifications have already been brought into use, and the number of more advanced services based on the intelligent network architecture increases continuously.
One supplementary service included in mobile communication systems is a closed user group (CUG). By means of the closed user group several different restrictions concerning the internal or external telecommunications can be defined for a selected group of subscribers. Available call restrictions include for example barring of incoming or outgoing calls and barring of long-distance or international calls. Closed user groups are typically applied in companies in which it is desirable to restrict the use of mobile stations given to employees mainly to professional purposes. In call set-up process closed user groups cause additional checks, on the basis of which call set-up either is continued normally or is discontinued due to call restrictions.
In closed user groups it is possible to allow some members of the closed user group to communicate with users outside the group by giving an outgoing access authorization to those members. Usually, such an outgoing access capability is provided only for a few members of the closed user group. The outgoing access capability is defined for each member or subscriber of the closed user group in a subscriber data base.
The WO 99/08468 defines a method of giving a call transfer possibility to some members of the closed user group. The basic idea of this patent application is to allow the transfer of a call to a specific number. The implementation of this feature has to be carried out for each subscriber in the corresponding subscriber data base.
However, in practice there is a need that all members or at least a group of the members of a closed user group can obtain outgoing access authorization for example with respect to numbers like numbers of authorities or some special service numbers outside the closed user group.